1. Field of the Invention
The present invention relates to a humidity detection sensor including a dielectric substance as a humidity sensing film and a method for manufacturing the same.
2. Description of the Related Art
As a humidity detection sensor used for measuring a humidity change, there is a capacitance type humidity detection sensor including a dielectric substance as a polymer humidity sensing film whose dielectric constant changes in response to an amount of absorbed or discharged water. The capacitance type humidity detection sensor includes a sensor section whose capacitance changes in response to humidity; and a reference section that keeps its capacitance constant regardless of humidity. The capacitance type humidity detection sensor converts the capacitance difference between the sensor section and the reference section to a voltage and outputs the voltage. Each of the sensor section and the reference section has a lamination structure in which a polymer humidity sensing film is interposed between a pair of electrodes. Such a humidity detection sensor is disclosed, for example, in PCT Japanese Translation Patent Publication No. 2003-516538.
As disclosed in PCT Japanese Translation Patent Publication No. 2003-516538, as the structure of the humidity detection sensor, there is a structure in which a pair of opposed comb electrodes are provided on the same plane and a humidity sensing film is provided on the pair of comb electrodes, or a structure in which a humidity sensing film is provided between a lower electrode formed on a board and an upper electrode provided on the lower electrode so as to face the lower electrode.
The structure in which the humidity sensing film is provided between the upper and lower electrodes is formed by laminating the lower electrode, the humidity sensing film, and the upper electrode in order, and thus it is possible to easily control the thickness and smoothness of the humidity sensing film as compared to the case where the humidity sensing film is provided on the comb electrodes provided on the same plane. Meanwhile, in the case of the parallel-plate structure in which the humidity sensing film is interposed between the upper and lower electrodes, the upper electrode is exposed, and thus a problem of humidity resistance, such as corrosion of the upper electrode due to water or the like, arises.
As a solution to the problem, it is conceivable to form a protective film on the upper electrode of the sensor section. However, as described in PCT Japanese Translation Patent Publication No. 2003-516538, in the parallel-plate structure in which the humidity sensing film is provided between the upper and lower electrodes, when the upper electrode is partially removed to partially expose the humidity sensing film, thereby smoothly supplying water molecules to the humidity sensing film, if a protective film is formed over the entire surface, external water molecules cannot smoothly be supplied to the humidity sensing film. Meanwhile, a method of selectively forming the protective film only on the upper electrode is conceivable. However, in this case, a problem of corrosion from side surfaces of the exposed upper electrode is considered.